Laser diode pumping of Nd:YAG lasers is well recognized for producing high efficiency, low threshold devices. Unfortunately, it is difficult and expensive to fabricate laser diode arrays with the proper power, bandwidth and center wavelengths to be useful for pumping Nd laser materials. In addition, usually the pumping diodes themselves are typically made of AlGaAs semiconductor material, and, therefore, have a naturally broad wavelength range over which they can operate. Another consideration is that accurate thermal control of the pumping diode junction temperature is required for efficient operation of the Nd:YAG laser due to the narrow absorption bandwidth at 808 nm. Such control is a cumbersome design constraint and adds complexity to the overall system. The narrow absorption line width also increases the difficulty of modeling both the inversion profile resulting from volumetric deposition of the polychromatic pump excitation, and the effects of anticipated spectral shifts in the pump source due to aging, see for example the article of R. Scheps and J. F. Myers, "Performance and Aging of a High Power 2-D Laser Diode Array", Appl. Opt, Vol. 29 (1990), p. 341.
With respect to using diode arrays as the pumping source, the additional aspect of the variation in the central wavelength and bandwidth from stripe to stripe must be considered. From a pragmatic viewpoint, the specification requiring a high power narrow band diode pumping array increases the cost of the semiconductor pump. Because in practice the diode pumping array is often the single most expensive component in the laser head, the total costs can easily become prohibitive. To address this issue, hosts for the Nd ion have been sought in which the width of the 800 nm absorption is increased. Two examples of such host materials are Nd:BEL, (see the article by R. Scheps et al., "End Pumped Nd:BEL Laser Performance" in Opt. Eng., Vol. 27 [1988], p. 830) and Nd:YVO.sub.4 (see the article of R. A Fields et al., "750 mW, 1.06.mu.m, cw TEM.sub.oo Output from a Nd:YVO.sub.4 Laser End Pumped by a Single 20 Stripe Diode Array" in Advances in Laser Science-III, American Institute of Physics Conference Proceedings, Atlantic City, NJ, Vol. 172 [1987], pp. 20-22) which both have been diode pumped and have a significantly broader absorption bandwidth than Nd:YAG.
Thus, there is a continuing need in the state of the art for an efficient Nd-doped laser material that can be diode pumped but is far less sensitive to the exact wavelength and bandwidth of the pump diodes than are the previously demonstrated Nd-doped laser materials.